Oxidative dehydrogenation, particularly oxidative dehydrogenation of n-butenes to make 1,3 butadiene is known. Process details are discussed at some length in Welch et al., Butadiene via oxidative dehydrogenation, Hydrocarbon Processing, November 1978, pp. 131-136. A high ratio of superheated steam to hydrocarbon in the feed supplies the necessary heat and increases the per pass yields by reducing partial pressures. Steam also acts as a heat sink in an adiabatic reaction system to moderate temperature rise during the intensely exothermic reaction. U.S. Pat. No. 7,034,195, to Schindler et al., discusses a two stage oxydehydrogenation arrangement at Col. 10, lines 38-53, but does not address the temperature control. U.S. Pat. No. 8,088,962, to Klanner et al., mentions multi-zone reactors at Col. 17, lines 51-56 in connection with 2-zone multiple catalyst tube fixed bed reactors. See, also, U.S. Pat. No. 6,998,504, to Unverricht et al. which recites tube-bundle reactors.
Fixed bed, adiabatic reactors are preferred over tube-bundle reactors because of their simple construction, low capital costs and low operating and maintenance costs as well as well established operational know-how with these reactors. In a traditional version of the oxidative dehydrogenation process, a large flow of steam is used to control the exotherm, typically in a steam to n-butene molar ratio of 12:1 or more. The large amounts of steam employed require large amounts of energy for superheating and vaporization as discussed hereinafter.
N-butene raw material for making butadiene is oftentimes scarce and difficult to obtain at prices suitable for commercial manufacturing operations. It is known in the art to dimerize ethylene to butene and use the recovered butene for manufacturing butadiene. U.S. Pat. No. 3,728,415 to Arganbright discloses producing butenes by dimerizing ethylene with a catalyst including palladium oxide with molybdenum oxide or tungsten oxide and using the product for dehydrogenation to make butadiene.
Other references of interest include the following: U.S. Pat. Nos. 3,911,042 and 3,969,429 to Belov et al. which disclose titanium/aluminum catalyzed dimerization of ethylene and note the product is useful for making butadiene; U.S. Pat. No. 7,488,857 to Johann et al. which discloses coproduction of butadiene and butene-1 from butane; and United States Patent Application Publication No. US 2011/0288308 to Grasset et al. which discloses ethylene dimerization with titanium/aluminum catalyst.
It is proposed in Japanese Patent Publication 2011-148720 to manufacture butadiene from ethylene by way of dimerizing ethylene followed by oxidative dehydrogenation using specified catalysts to minimize impact of various impurities. The method proposed includes the following steps (I) and (II): a step (I) for producing n-butene essentially free of isobutene by dimerizing ethylene at a reaction temperature of 150 to 400° C. in the presence of a catalyst consisting of nickel, alumina, and silica having a nickel content of 0.0001 to 1 wt. %; and a step (II) for producing butadiene by performing an oxidative dehydrogenation reaction on the n-butene obtained in said step (I) with oxygen at a reaction temperature of 300 to 600° C. in the presence of a complex metal oxide comprising molybdenum and bismuth as essential ingredients.
Existing oxidative dehydrogenation processes can be relatively impurity-sensitive and energy intensive due to the large recirculation rates of steam and nitrogen employed; moreover, there is an ever-present need to increase conversions and yields, especially conversions and yields per pass.